Lack of power when hot

[Japscrap_96]

I own a 96 240sx manual with 193k miles on it. I'm having a bery specific problem with it. When I first start the car it drives awesome for the first 30-50 mins, after that it begins to lose power. For example, if I come to red light and want to take off the car barely moves (no pull) but the RPM goes up. This same thing happens on second and third. It takes really long to catch speed. Even if I floor it!
It's alsmost as if the clutch was slipping. Two weeks a go a technician friend of mine replaced the clutch for me, but the problem didn't go away. We scanned the car and got 5 codes (p0304, p1447, p0446, p0440, and p0325) The most important ones where misfire on cylinder 4 and knock sensor. So last night I went ahead and did a tune up to the car. I bought NGK plugs and wires, new cap and rotor, and bought a knock sensor. The misfire went away, the cap was cracked. I drove the car that night for an hour and 10 mins (the longest its lasted without losing 50% power or so) I called my buddy and he said it could be an O2 sensor or a coolant temp sensor. So I bought those two and put them in, I also went from mid grade to premium gas. The car drove like a dream. I even did some skids. An hour into the fun drive the car lost power and was barely moving. Now I'm here sitting trying to figure out what's wrong with the car. I would really appreciate it if you could help me out. Thank you so much.

[dadymurano]

I nthought most of those codes (from memory) was the evap fuel sys malfunctioning. It's like a closed loop with gas going from the tank to your injectors with fumes and such rerouted back to the gas tank for recirculation.

I may be far off but if you're reading the codes and logically diagnosing the problem you're on the right track.

[Japscrap_96]

Yeah most of them at EVAP codes wich I don't really care about. I don't believe the EVAP affects the performance of the car. I still don't know why the car lacks power when hot. It's as if the clutch was slipping but that can't be it because I just replaced the clutch.

[Harrythook]

If its a stock motor setup with a cat you might have a little back-pressure issue. Run the car "fat" or rich you overload the cat, which in turn creates excess pressure in the exhaust. This problem gets worse as you drive it, even if the car is in tune right now.
Recheck your codes, refer back to the service manual to see what you have. You can attempt to release exhaust pressure by pulling the O2 when the fault occurs, and running with exhaust leak. But that takes the O2 out of the system so you might get a slightly faulted diagnosis.

[Japscrap_96]

Yes it's a stock car. I was thinking about straight piping the car no cat no resonator and no muffler. Thank you for your help. I'm gonna delete the cat and see what happens.

[asoomal]

What you really need to do is hook up an OBDII scan tool and monitor it while driving.

If the tachometer still shows the rpm going up and the car isn't moving, it's definitely a drivetrain issue.

[Japscrap_96]

How could it be a drivetrain isue? I mean the car drives amazingly, for the first 40-50 mins then it starts to like "feel like the clutch is slipping" but the clutch is brand new and was installed by a technician. Little by little the car starts to lose power. I believe it has something with the catalytic and back pressure like Harrythook mentioned. I haven't removed the cat yet, but I did perform a compression test and it went awesome!! Got 185psi across!!! In case it were a drive train issue what do you think it would be? I almost for got to say that I do have a OBII scan tool and everything is fine but code p1447 wich is evap. I'm not really worried about that since Im not planning on registering the car any time soon. Thank God for DL plates. And thank you for your help.

[asoomal]

Does it still have the clutch slip like feeling?

[Japscrap_96]

Yes it still feels like its slipping, but I don't get why it doesn't do it when I first start the car and drive it for the first 50 mins. Haven't cut out the cat.

[asoomal]

If it still feels like slipping, then it has to be a drivetrain issue.

If the exhaust was clogged, the RPMs wouldn't go up like that. It would just bog the whole time.

What was replaced and serviced during the clutch replacement? Was the rear main seal also replaced?

Was the system properly bled? Removed clutch damper?

Typically, when the vehicle suffers from clutch slippage as the vehicle warms up, it is either clutch master cylinder or slave cylinder related.

[Japscrap_96]

Yes the system was bled and we also replaced the rear seal. We installed a new slave cylinder because the old one was leaking. You're saying I should remove the damper? Thank you for helping me.

[asoomal]

The damper makes the system difficult to bleed at times, so the system may have not been fully bled.

Also, what condition is the clutch master in? Has it ever been replaced?

[Japscrap_96]

I just researched a little about deleting the damper but I'm not really sure about doing it nor how to do it. The master cylinder looks fairly new. My buddy the mechanic said the master looked fine. Any tutorials on how to delete the damper? Do you recomend doing so? Again thank you for the help. I'm
Learning a lot with you.

[asoomal]

http://www.nicoclub.com/archives/clutch ... moval.html

Also, where is the friction point of the clutch?

[Japscrap_96]

Thank you for the link. I'm gonna check that out right now. The friction point feels to be up top. You don't have to press the clutch all the way at the bottom for it to grab. I don't know if you understand me.

[asoomal]

Adjust it so the friction point is lower, the clutch might not be engaging all the way.

[Japscrap_96]

To be honest I'm not sure my car has a clutch damper. I don't remember seeing it. My buddy the mechanic doesn't remember seeing it either. He also told me the MAF could me messed up. I'm gonna clean the MAF, cut out my cat, putting a 3 inch exhaust, see if my damper is there, if it isn't im going to delete it, bleed the clutch and I'll come back Monday to tell you about my results. Thank you for the help

[Lobo240sx]

Starting to think your Exhaust manifold gasket could have a small leak. After blowing 2 exhaust gaskets with similar symptoms, I'm switching to a Copper Gasket this weekend. I'd check that out and your header.